1. Field of the Invention
The invention relates to a method and an apparatus for the noninvasive determination of a patient's blood pressure. In the method, an electrical cardiac-potential measurement signal and a pulse measurement signal of a pulse pressure wave which, starting from the heart, propagates within the blood vessels are recorded at a pulse-feeling location; and, from the electrical measurement signal and the pulse measurement signal, a propagating time is determined of the pulse pressure wave between the heart and the pulse-feeling location. The apparatus comprises an ECG sensor for the detection of an electrical cardiac-potential measurement signal, a pulse sensor for the detection of a pulse measurement signal of a pulse pressure wave which, starting from the heart, propagates within the blood vessels to a pulse-feeling position where the pulse sensor is disposed; and an evaluation unit for determining, from the electrical measurement signal and the pulse measurement signal, a propagating time of the pulse pressure wave between the heart and the pulse-feeling position.
2. Background Art
A method of the generic type has been known from WO98/25516 A1 and an apparatus of the species from U.S. Pat. No. 5,709,212. In the known method, blood pressure is computed as a linear function of the determined propagating time of the pulse pressure wave; in the known apparatus, however, it is computed as a quadratic function of a pulse-pressure-wave velocity i.e., substantially of the reciprocal value of the determined propagating time.
DE 102 49 863 A1 also describes a blood pressure determination method and apparatus of the generic type, with any details on the function interrelationship between the determined propagating time of the pulse pressure wave and blood pressure missing.
U.S. Pat. No. 6,599,251 B2 and DE 100 61 189 A1 further disclose methods of noninvasive blood pressure determination, determining a difference in propagating time between two pulse pressure waves which are recorded at two different pulse-feeling locations. The further evaluation uses a non-linear interrelationship between the determined difference of propagating time and required blood pressure. Mention is made of a logarithmic, a potential and an exponential interrelationship.
All those known blood pressure determination methods and apparatuses are in part more suitable than conventional methods and apparatuses which are based for example on the Riva-Rocci principle. Inflation of an arm cuff can be dropped, precluding any undesirable effect, accompanied there-with, on the circuit and on the blood pressure to be measured. Moreover, it is less interfering with a patient. Nevertheless, the mentioned, familiar blood pressure determination methods and apparatuses sometimes furnish blood pressure values that are too vague.